Patent Specification EP 1 232 008 B1 shows an elevator installation with an absolute positioning system. This absolute positioning system comprises a camera, which is arranged at an elevator car and is used for the purpose of generating images of shaft material or the surface structure of this shaft material. Regarded as shaft material are not only guide rails, shaft doors and other elevator components, which are arranged in stationary position in the shaft, but also shaft walls bounding the shaft. The shaft material forms, in its entirety, a surface structure which extends substantially along the travel path of the elevator car. This surface structure continuously changes so that each generated image is unique and can serve as an indicator for a position of the elevator car. The camera generates references images of the surface structure in a learning travel. An evaluating unit connected with the camera assigns to these reference images a position in the shaft and files the references images as well as the associated position values on a storage medium. In normal operation, an absolute position of the elevator car can now be determined by the evaluating unit on the basis of comparison of the images, which are continuously generated by the camera, with the filed reference images.
In the absolute positioning system according to EP 1 232 008 B1, by comparison with other absolute positioning systems there is no need for an additional code carrier for investigating the position of the elevator car. Nevertheless, in practice such an absolute positioning system could never be successful, since determination of the position of the elevator car on the basis of evaluation of the surface structure has proved to be insufficiently reliable.